The general objective of our research is to study the biological foundations of human language. We aim to investigate language and its formal architecture, as well as its representation in the brain, by studying languages which have arisen outside of the mainstream of spoken languages, the visual-gestural language of deaf people. For the form of its grammatical devices, the modality in which a language develops makes a crucial difference. The use of space in the service of syntax is the most highly modality-determined aspect of American Sign Language. One of the central issues in the renewal grant is the consequences of the spatial realization of syntactic function on mental representations for language, and on the nature of language representation in the brain. We proceed along three major lines of inquiry: I. On-line Processing of ASL Spatial Syntax. The area where ASL is most clearly conditioned by the visual modality is in the spatialized mechanisms for conveying syntax and discourse. ASL thus provides a critical vehicle by which to investigate language processing. Two uses of space within sign language, for spatially organized syntax and for topological representations of space itself, have very different implications for processing. We use on-line techniques to provide a rigorous assessment of moment to moment construction of these different linguistic representations as sentences are parsed. II. The Interplay between Spatial Language and Spatial Cognition. We investigate modality effects from the converging perspectives of universals of visuospatial languages and their spatial cognitive underpinnings. We examine formal devices for spatially organized syntax and spatial mapping across ASL and Chinese Sign Language. In sign language processing, spatial perception, memory, and spatial transformations are complex prerequisites to grammatical processing. We propose an intensive investigation of the interplay between spatial language and its spatial cognitive underpinnings. III. Hemispheric Specialization in Deaf Signers. Language and spatial representation are attributes for which the two cerebral hemispheres in hearing people show different predominant functioning. We propose experiments that help illuminate the nature of hemispheric specialization for sign language and for its cognitive prerequisites. We propose studies of hemispheric specialization for spatial cognitive functions in deaf and hearing signers. We then investigate specialization for aspects of sign language structures are unique to a visual-gestural language, including a differentiation between two uses of space in the language: the use of space for syntax and the use of space for mapping. These experiments allow us to understand how linguistic and modality factors determine the specialized capacities of the two cerebral hemispheres.